The present invention relates to an excavation and compaction equipment for the construction of piles.
From the European patent EP 0 228 138 it is known an excavation and compaction equipment for the construction of piles comprising an antenna, a rotary table slidingly mounted along the antenna, a drilling rod actuated by the rotary table, and a tool, which is mounted at a lower end of the drilling rod itself.
The tool comprises, in its turn, a central body with an external diameter equal to an external diameter of the rod, an excavation screw integral with the central body, and a displacer element arranged along the rod immediately on the screw for compacting the walls of the excavation during the drilling.
As it is also described in the patent, the equipment undergoes a torsional moment on the drilling rod and a thrust on the excavation screw relatively elevated because the mass of the soil to be compacted during the excavation by the displacer element is of significant relevance and exerts also a strong resistance to the advancement of the tool in the soil itself. A similar solicitation brings to the need for making an equipment of huge size and, also, to the need of adequate motorizations, whose power, however, is fully used only during the drilling/compaction phase, but not during the extraction of the tool from the excavation, that is during the filling by means of concrete injection through the tool itself.
When a pile is carried out according to this technology without removal of soil, it is important to obtain a good consolidation of the walls of the excavation and a good anchoring of the pile in the soil.
In this regard, for increasing the contact surface between pile and soil, a screw groove is carried out in the cylindrical wall creating the so-called “screw displacement pile” or screw pile. During the casting phase, the concrete flows in all the cavity by filling also the helical grooving which has been just grooved in the soil, giving to the pile a screwed shape which improves the anchoring to the soil and therefore its relative carrying capacity.
Furthermore, the screw pile permits a huge saving on the total quantity of the concrete used because with the same carrying capacity the diameter of the central shaft can be appreciably lower with respect to the one of the piles compacted with a cylindrical surface.
From the European patent EP 1 277 887 B1 it is known an equipment for constructing screw piles, but the carrying out of the compaction during the descent phase falls in the above mentioned drawbacks (big thrusts and torques required contemporarily for the advancement, machines having a significant tonnage for bearing the enormous thrusts). Furthermore, the tooth carries out the grooving both during the descent and during the ascent phase when filling with concrete, by increasing at least the relative consumption and the possibility of ostacles or breakings during the descent. On the other hand, during the ascent, the concrete immediately fills the grooving giving to the pile the screw shape, during the descent the groove is probably filled by the following compaction giving thus to the excavation wall a non-homogeneous compaction surface.
From the European patent EP 1726718 A1 it is known the possibility of carrying out piles through compaction of the soil during the phase of ascent with inversion of the rotation direction, but this does not provide for the possibility of carrying out screw piles.
The standard tools for the compaction in advancement are characterized in that they all have a lower conical tract necessary for the first penetration and enlarging of the soil. This part is provided with screw which makes the material to go back up to the upper tract (characterized in that it has the maximum diameter) until it generates the compaction at the desired diameter. During the ascent, these tools must absolutely continue rotating in the same direction of the advancement phase, because otherwise the soil contained in the conical tract, being in the lower part of the casting, would contaminate the casting drastically reducing the strength of the pile obtained. On the other hand, the technique of tensioned compaction requires a counter-rotation for separating the part of the casting from the one wherein it is contained the soil to be compacted.